Soil rot can be a serious problem in the production of sweet potatoes in Kansas. Affected plants develop a decay of the rootlets and malformation and pitting of the fleshy roots. The rootlets of infected plants may be injured so severely that the plants remain stunted. Fleshy roots often remain below market size and may be so malformed as to be unsalable.

Infections of the fleshy roots originate through infected lateral rootlets and may occur when the sweet potatoes are still small or later when they are more mature. Newly infected areas on the larger stems or fleshy roots develop dark, water-soaked lesions that are more or less circular. The infections extend only a limited distance into the tissues but penetrate sufficiently deep to injure the water- and food- conducting tissues.

DISEASE CYCLE

The organism Streptomyces ipomoea, which incites soil rot, survives in the soil indefinitely. The disease is more severe in alkaline soils.

CONTROL

Soil rot is difficult to control in fields where it has become established. This organism is not dependent on sweet potato plants for continued existence and can live from year to year on decaying organic matter in the soil. Rotating crops and keeping sweet potatoes off infested fields tends to reduce but does not rid fields of the organism. Be sure to select mother potatoes free from soil rot. The organism can be spread from infected bedding plants to the slips and on to noninfested soil. Be sure to bed in areas free of the disease. Plant slips in fields where soil rot has not occurred or in soils that have been fumigated. The disease is inhibited in soils where the pH is 5.0 to 5.2. Raising the pH by liming tends to increase the severity of the disease. Application of sulfur to alkaline soils may be helpful, but be sure to consult with a soil specialist before applying sulfur. Soil fumigation will help to control this disease, but it is very expensive.

Web updated 9/01/06
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